Hyperphosphorylated tau targeting human serum albumin Fusion protein as therapeutics for Alzheimer's diseases.

Introduction: Neurofibrillary tangles (NFTs) are composed of hyperphosphorylated forms of microtubule-associated protein tau (Tau), which is responsible for neurodegeneration in Alzheimer's disease (AD). The hippocampal region has been a major focus of AD research because the deposits of phosphorylated tau protein in these regions are correlated with early memory deficits. Despite extensive studies, therapeutic strategies to reduce tau hyperphosphorylation and NFTs deposition remain unclear. AL04, a recently developed recombinant fusion protein comprising Cystatin C, human serum albumin, and a novel blood brain barrier (BBB) penetrating peptide, is currently under investigation. Previous studies have demonstrated its effectiveness in reducing amyloid beta plaques in AD mouse model. Methods: In this study, we investigated the effects of AL04 on lowering hyperphosphorylated tau and NFTs in JNPL3 mouse model harboring human tau-P301L mutation. 3-month-old female mice intraperitoneally received AL04 (5 mg/kg) or PBS treatment every other week for 24 weeks. We used confocal microscopy and western blot to visualize and analyze changes in hyperphosphorylated tau Ser202/Thr205 labeled with AT8 antibody in the brain. Results: We found that the AL04 treatment decreases hyperphosphorylated tau at PP2A-sensitive epitope Ser202/Thr205 in the hippocampus of the brain. In the brain lysates of AL04 treated mice, we observed the reduction of I2PP2A, inhibitor of PP2A, and the induction of autophagy receptor proteins such as SQSTM-1/p62 and OPTN. Conclusion: Our data suggests that AL04 can be used as an AD prophylactic/therapeutic agent as it lowers the hyperphosphorylated tau by downregulating I2PP2A. We also propose that AL04 can induce the degradation of hyperphosphorylated tau aggregates through the upregulation of the autophagy pathway.